Fuel supply systems for gas turbine engines

ABSTRACT

A fuel supply system for a gas turbine engine has a positivedisplacement pump driven by the engine a valve downstream of the pump having an inlet and two outlets. A control element varies flow through the two outlets simultaneously. One of the outlets supplies fuel to the engine and the other outlet communicates with a pressure-responsive spill valve with the low pressure side of the pump. The spill valve arrangement is such that the pressures at the valve outlets remain substantially equal.

United States Patent 1 Lewis [4 1 Nov. 6, 1973 p [75] Inventor:

[54] FUEL SUPPLY SYSTEMS FOR GAS TURBINE ENGINES Geoffrey Arthur Lewis,Solihull, Warwickshire, England [73] Assignee: Joseph Lucas (Industries)Limited,

Birmingham, England [22] Filed: Nov. 5, 1971 [2]] Appl. No.: 195,970

[30] Foreign Application Priority Data Nov. 7, 1970 Great Britain53,091/70 [52] US. 60/3928 R, 137/117 [51] Int. Cl. F02c 9/10 [58] Fieldof Search 60/3928; 137/117 [56] 1 References Cited UNITED STATES PATENTS3,078,670 2/1963 Werner 60/3928 R 3,381,470 5/1968 Hammerstein 60/3928 R3,498,058 3/1970 Greunc 60/3928 3,616,647 11/1971 Johnson 60/3928Primary Examiner-Clarence R. Gordon Attorney-Holman & Stern [57]ABSTRACT A fuel supply system for a gas turbine engine has apositive-displacement pump driven by the engine a valve downstream ofthe pump having an inlet and two outlets. A control element varies flowthrough the two outlets simultaneously. One of the outlets supplies fuelto the engine and the other outlet communicates with a pressureresponsive spill valve with the low pressure side of the pump. The spillvalve arrangement is such that the pressures at the valve outlets remainsubstantially equal.

16 Claims, 3 Drawing Figures Patented Nov. 6, 1973 2 Sheets-Sheet 1FIGI;

Patented Nov. 6, 1973 2 Shets-5heet 2 FIGS.

FUEL SUPPLY SYSTEMS FOR GAS TURBINE ENGINES This invention relates tofuel supply systems for gas turbine engines and has as an object toprovide such a system in a convenient form.

A fuel supply system in accordance with the invention comprises a fixeddisplacement fuel pump driven in use, at a speed proportional to theengine speed; a valve including a chamber having an inlet connected tothe outlet of the pump and first and second outlets and a controlelement variably positionable between said outlets so as to vary theeffective flow area of the two outlets simultaneously; a pressurecontrol unit sensitive to the pressures at said two outlets and arrangedto spill sufficient fuel from the first outlet to maintain the ratio ofsaid pressures substantially constant; and means for positioning thecontrol element of the valve in accordance with the fuel requirement ofthe engine.

In the accompanying drawings, FIGS. 1 to 3 are diagrammatic views ofthree examples of the invention, the example of FIG. 3 also showing theconnections to an associated gas turbine engine.

FIG. 1 is mechanically the simplest form of the invention and the systemshown comprises a fixed displace ment pump which is driven at a speedproportional to the engine speed, a valve 11, and a pressure controlunit 12 and an electrical actuator 13 with a control circuit 14 for thevalve.

The valve 11 includes a chamber 15 with an inlet 16 into which the fullflow from the pump 10 passes. The chamber has first and second outlets17, 18 respectively and a control element 19 in the form of an armpivotable at one end and extending between the outlets 17, 18 adjacentthe opposite end. The actuator 13 positions the element 19 so that theeffective area of both outlets can be varied simultaneously. Movement ofthe element 19 reduces the effective area of one outlet and increasesthe effective area of the other. A pairof adjustable stops 20, 21 areprovided for limiting movement of the element 19 towards the outlets 17,18 respectively. i

The pressure control unit is in the form of a chamber divided into twoby a diaphragm unit 22. There are connections from the outlets 17, 18 tothis chamber on opposite sides of the diaphragm unit. On the side of thediaphragmunit to which the outlet 17 is connected there is an outlet 23which is controlled by the diaphragm unit and this outlet 23 isconnected to the low pressure side of the pump 10. A light spring 24 isprovided on the other side of the diaphragm unit to urge the lattertowards the outlet 23.

The pressure control unit is such that, over the 1 greater part of therange of pressures in question the diaphragm unit is so positioned thatthe pressures on both sides thereof are substantially equal, therebymaintaining the ratio of such pressure substantially constant at unity.

At the lower end of the pressure range the effect of the spring 24becomes significant and the pressure at outlet 18 becomes higher thanthat at outlet 17.

Outlet 18 is connected to the burner manifolds of the engine with theresult that, for any given position of the control element 19, the rateat which fuel flows to the engine is directly proportional to the enginespeed, ex-

cept at the lower end of the engine speed range. Whereas in the exampledescribed, the pressures at outlets l7 and 18 are maintained equal, thepressures on the control element 19 are balanced and this simplifies theactuator considerably by eliminating the need for a closed loopservo-mechanism.

In the modification shown in FIG. 2 a top speed governor has beenincorporated in the valve 111 which is otherwise identical to the valve11. This enables the top-speed governing function of the control circuit114 to be omitted. The governor relies on the fact that the pressureloss through the outlet 118 is proportional to the square of the enginespeed for any given position of the control element 119. A diaphragmunit is mounted in an opening in the wall of the chamber 115. A cover126 over the diaphragm unit 125 has its interior connected to the outlet118. A spring l27'urges the diaphragm unit in the same direction as thepressure in the cover 126. 7

An abutment 128 carried by the: diaphragm unit 125 is engageable withthe control element 119 to move the latter towards the outlet 118 whenthe pressure drop is excessive.

The embodiment shown in FIG. .3 is a complete combined accleration andspeed control. In this case the control element 219 of the valve 211 isspring loaded towards the outlet 217 by a spring 229. An adjustable stop230 is provided for the spring 227 of the governor and this stop ismovable by a manual speed control lever 231. In this case the unit 212which replaces the unit 12 is springless so that true proportional flowcharacteristics are obtained. The speed limit set by the governormechanism varies in dependence on the setting of lever 231. In steadyrunning conditions the moment of the force applied to the controlelement .219 by the abutment 228 is exactly counter-balanced by themoment of the force applied by spring 229.

For acceleration control, there is a variable stop 232 to coact with thecontrol element 219. This stop 232 is positionable in accordance withair pressure conditions arising in the engine compressor and is engagedwith a wedge-shaped cam 233 movable by a resilient bellows unit 234 towhich an air pressure signal derived from the compressor is applied todisplace the cam 233. The air pressure applied to the bellows unit 234is obtained by connecting an air-potentiometer consisting of two flowrestrictor 235, 236 between pressure tappings in the engine air intake(P and high pressure side of the compressor (P The bellows unit 234 isconnected to the potentiometer between the two flow restrictors.

During rapid acceleration the control element 219 abuts the stop 232 andis thus positioned in accordance with the compressor pressure conditionsto avoid stalling of the compressor.

The spring 24 in the unit 12 can be omitted to give substantially trueproportional flow characteristics, although the fact that the pressureat outlet 17 does not act over the whole of the left hand side of thediaphragm 22, owing to the outlet 23, may thenbecome of significance.The inclusion of a light spring 24 can thus be of considerablesignificance in the determination of the flow characteristics ofthesystern and these characteristics can be varied by choice of theproperties of the spring.

I claim:

1. A fuel supply system for a gas turbine engine, comprising a fixeddisplacement pump driven in use, at a speed proportional to the enginespeed; a valve including a chamer having an inlet connected to theoutlet of the pump and first and second outlets and a control elementvariably positionable between said outlets so as to vary the effectiveflow area of the two outlets simultanously; a pressure control unitsensitive to the pressures at said two outlets and arranged to spillsufficient fuel from the first outlet to maintain the ratio of saidpressures substantially constant; and means for positioning the controlelementof the valve in accordance with the fuel requirement of theengine.

2. A system as claimed in claim 1 in which the means for positioning thecontrol element comprises an electrical actuator.

3. A system as claimed in claim 1 in which the said second outlet isconnected to the burners of the engine.

4. A system as claimed in claim 1 in which the control element comprisesan arm pivotally mounted in said chamber.

5. A system as claimed in claim 1 in which movement of the controlelement causes the flow area of one of the outlets to be increased andthe flow area of the other outlet to be decreased.

'6. A system as claimed in claim 1 in which the pressure control unitcomprises a diaphram unit subjected on opposite sides to the pressuresat the respective outlet and a port communicating with a low pressureside of the pump, said diaphragm unit acting to control flow from saidfirst outlet to said port.

7. A system as claimed in claim 6 which includes a means biasing thediaphragm unit in a direction to shut said port.

8. A system as claimed in claim 1 in which the ratio of said pressuresis maintained substantially at unity.

9. A system as claimed in claim 3 which includes means for limitingmovement of said control element in response to said positioning means.

10. A system as claimed in claim 9 in which said movement limiting meanscomprises a device responsive to an increase in the pressure drop acrosssaid second outlet to limit movement of said control element in adirection to increase flow throughsaid second outlet.

11. A system as claimed in claim 10 in which said device comprises adiaphragm subjected on its respective sides to the pressures upstreamand downstream of said second outlet, and an abutment member movable bysaid diaphragm and engageable with said control member.

12. A system as claimed in claim 9 in which said movement limiting meanscomprises a stop engageable by said control member and movable inresponse to a difference in the pressures across a compressor of theengine.

13. A system as claimed in claim 12 in which said stop is operable tolimit flow through said second outlet.

14. A system as claimed in claim 9 which includes a device responsive toan increase in the pressure drop across said second outlet to limitmovement of said control element in a direction to increase flow throughsaid second outlet.

15. A system as claimed in claim 14 in which the said device comprises adiaphragm subjected on its respective sides to the pressures upstreamand downstream of said second outlet, and an abutment member movable bysaid diaphragm and engageable with said control member.

16. A system as claimed in claim 15 in which the means for positioningsaid control element comprises first biasing means urging said controlelement towards said abutment member, second biasing means urging saiddiaphragm in a direction to permit an increased flow through said secondoutlet and means for varying the force applied by said second biasingmeans.

1. A fuel supply system for a gas turbine engine, comprising a fixeddisplacement pump driven in use, at a speed proportional to the enginespeed; a valve including a chamer having an inlet connected to theoutlet of the pump and first and second outlets and a control elementvariably positionable between said outlets so as to vary the effectiveflow area of the two outlets simultanously; a pressure conTrol unitsensitive to the pressures at said two outlets and arranged to spillsufficient fuel from the first outlet to maintain the ratio of saidpressures substantially constant; and means for positioning the controlelement of the valve in accordance with the fuel requirement of theengine.
 2. A system as claimed in claim 1 in which the means forpositioning the control element comprises an electrical actuator.
 3. Asystem as claimed in claim 1 in which the said second outlet isconnected to the burners of the engine.
 4. A system as claimed in claim1 in which the control element comprises an arm pivotally mounted insaid chamber.
 5. A system as claimed in claim 1 in which movement of thecontrol element causes the flow area of one of the outlets to beincreased and the flow area of the other outlet to be decreased.
 6. Asystem as claimed in claim 1 in which the pressure control unitcomprises a diaphram unit subjected on opposite sides to the pressuresat the respective outlet and a port communicating with a low pressureside of the pump, said diaphragm unit acting to control flow from saidfirst outlet to said port.
 7. A system as claimed in claim 6 whichincludes a means biasing the diaphragm unit in a direction to shut saidport.
 8. A system as claimed in claim 1 in which the ratio of saidpressures is maintained substantially at unity.
 9. A system as claimedin claim 3 which includes means for limiting movement of said controlelement in response to said positioning means.
 10. A system as claimedin claim 9 in which said movement limiting means comprises a deviceresponsive to an increase in the pressure drop across said second outletto limit movement of said control element in a direction to increaseflow through said second outlet.
 11. A system as claimed in claim 10 inwhich said device comprises a diaphragm subjected on its respectivesides to the pressures upstream and downstream of said second outlet,and an abutment member movable by said diaphragm and engageable withsaid control member.
 12. A system as claimed in claim 9 in which saidmovement limiting means comprises a stop engageable by said controlmember and movable in response to a difference in the pressures across acompressor of the engine.
 13. A system as claimed in claim 12 in whichsaid stop is operable to limit flow through said second outlet.
 14. Asystem as claimed in claim 9 which includes a device responsive to anincrease in the pressure drop across said second outlet to limitmovement of said control element in a direction to increase flow throughsaid second outlet.
 15. A system as claimed in claim 14 in which thesaid device comprises a diaphragm subjected on its respective sides tothe pressures upstream and downstream of said second outlet, and anabutment member movable by said diaphragm and engageable with saidcontrol member.
 16. A system as claimed in claim 15 in which the meansfor positioning said control element comprises first biasing meansurging said control element towards said abutment member, second biasingmeans urging said diaphragm in a direction to permit an increased flowthrough said second outlet and means for varying the force applied bysaid second biasing means.